Apparatus and method for separation of wet particles

ABSTRACT

An apparatus and a process for separating particles in a slurry based on different physical, magnetic and/or chemical properties of the particles, the slurry including a mixture of solid particles and/or liqid particles which are immiscible in the slurry. The process comprises: 
     tangentially introducing a stream of the slurry into a cylindrical chamber having a cylindrical inner wall with sufficient volume and pressure to develop a vortex in the slurry which extends downwardly from an upper end; 
     introducing air into the stream during at least a portion of its upward travel, the air being introduced to the stream through means located at the chamber inner wall and for developing the air bubbles which move into the stream; 
     the chamber being of a height sufficient to allow the stream to develop into a whirlpool at the chamber upper end; 
     directing the whirlpool stream outwardly at the open end into a catch basin surrounding the open end; and 
     separating the floating air bubbles with lighter hydrophobic particles from the heavier particles by collecting outwardly floating air bubbles with an upper zone of the catch basin.

FIELD OF THE INVENTION

This invention relates a to process and apparatus for separatingparticles in a slurry where the particles possess different physical,magnetic and/or chemical properties. More particularly, the process andapparatus is very effective in separating liquid hydrocarbons from waterwhich may contain solids, separation of one or more solids from liquids,separation of mineral ores which may be of ferri-, ferro- and/orpara-magnetic properties.

BACKGROUND OF THE INVENTION

Flotation systems are important unit operations in process engineeringtechnology that were developed to separate particulate constituents fromslurries. Flotation is a process whereby air is bubbled through asuspension of finely dispersed particles, and the hydrophobic particlesare separated from the remaining slurry by attachment to the airbubbles. The air bubble/particle aggregate, formed by adhesion of thebubble to the hydrophobic particles, is generally less dense than theslurry, thus causing the aggregate to rise to the surface of theflotation vessel. Separation of the hydrophobic particles is thereforeaccomplished by separating the upper layer of the slurry which is in theform of a froth or foam, from the remaining liquid.

The fundamental step in froth flotation involves air bubble/particlecontact for a sufficient time to allow the particle to rupture theair-liquid film and thus establish attachment. The total time requiredfor this process is the sum of contact time and induction time, wherecontact time is dependent on bubble/particle motion and on thehydrodynamics of the system, whereas induction time is controlled by thesurface chemistry properties of the bubble and particle.

However, flotation separation has certain limitations that render itinefficient in many applications. Particularly, in the past it has beenthought that flotation is not very effective for the recovery of fineparticles (less than 10 microns in diameter). This can be a seriouslimitation, especially in the separation of fine minerals. Anexplanation for this low recovery is that the particle's inertia is sosmall that particle penetration of the air-liquid film is inhibited,thus resulting in low rates of attachment to the bubbles. Furthermore,flotation has never been relied on as a process to effect separation ofhydrocarbons in a slurry.

A further limitation of conventional flotation systems is that nominalretention times in the order of several minutes are required to achievesuccessful separation. However, it has been shown that airbubble/particle attachment is frequently in the order of milliseconds,therefore indicating that the rate of separation is mostly limited bybubble-to-particle collisions and/or transport rather than by otherfactors. As such, these long retention times severely limit plantcapacity and require the construction of relatively large and expensiveequipment.

Air-sparged hydrocyclones (hereinafter "ASH") were developed to overcomethese two limitations of conventional flotation systems. Early systemssuch as disclosed in Russian Patent 692634 (Oct. 25, 1979) and in GermanPatent 1,175,621 (Aug. 13, 1964) were relied on to effect separation ina Centrifugal field by introducing air bubbles in the swirling stream.Refinements on this concept have been made such as exemplified in U.S.Pat. Nos. 4,279,743, 4,397,741, 4,399,027 and 4,744,890 which disclosecertain improvements in ASH units. ASHs combine flotation separationprinciples with centrifugal forces to achieve successful separation offiner particles with retention times in the order of several seconds. Acontrolled high force field is established in the ASH by causing theslurry to flow in a swirling fashion, thereby increasing the inertia ofthe finer particles. Also, high density, small diameter air bubbles areforced through the slurry to increase collision rates with theparticles. The net result is flotation rates with retention timesapproaching intrinsic bubble attachment times. This corresponds to acapacity that is at least 100 to 300 times the capacity of aconventional mechanical or column flotation unit.

In ASH flotation, fluid pressure energy is used to create rotationalfluid motion (swirling motion). This is done by feeding the slurrytangentially through a conventional cyclone header into a cylindricalvessel. A swirl flow of a certain thickness is developed in thecircumferential direction along the vessel wall, and is dischargedthrough an annular opening created between the vessel wall and apedestal located axially on the vessel's bottom.

Air is introduced into the ASH through the jacketed porous vessel walls,and is sheared into numerous small bubbles by the high velocity swirlflow of the slurry. Hydrophobic particles in the slurry collide with theair bubbles, attach to the bubbles, and are transported radially by thebubbles into a froth phase that forms in the cylindrical axis. The frothphase is supported and constrained by the pedestal at the bottom of thevessel, thus forcing the froth to move upward towards the vortex finderof the cyclone header, and to be discharged as an overflow product. Thehydrophillic particles, on the other hand, generally remain in theslurry phase, and thus continue to move in a swirling direction alongthe porous vessel wall until they are discharged with the slurry phasethrough the annulus opening between the vessel wall and the pedestal.

It is important to note that the swirling motion of the slurry along thevessel wall forms a "swirl-layer" that is distinguishable from the forthphase at the center of the cylindrical vessel. One importantcharacteristic of the swirl-layer is that it has a net axial velocitytoward the underflow discharge annulus between the vessel wall and thefroth pedestal. The thickness of the swirl-layer is generally 8% to 12%of the vessel radius, and it increases with increasing air flow rate andwith axial distance from the cyclone header, being greatest at theunderflow discharge annulus.

The size and motion features of the froth formed along the cylindricalvessel's axis are dependent on operating conditions and feedcharacteristics. Between the swirl-layer and the froth core, thereexists a transition region for the slurry, where the net velocity in theaxial direction is either zero, or in the same direction as the slurryphase. The latter condition exists where the froth core is relativelysmall, thus leaving a large gap between the swirl-layer and the frothcore track is filled with slurry. The most desirable condition is whenthe transition region is minimal, that is when the froth core is largeenough to leave little space between it and the swirl-layer.

A pressure drop is created in the froth core, between the froth pedestaland the vortex finder outlet located axially at the top of the vessel.This pressure drop is the force that actually drives the froth axiallyupwards. There are three factors that affect the pressure drop in theforth core:

1. restriction of the slurry flow to the underflow discharge annulus;

2. restriction of the froth transport to the overflow vortex finderopening; and

3. continuous supply of fresh froth to the froth core from theswirl-layer.

Factors 1 and 2 are in turn dependent on the particular application andcan be adjusted during the operation. Factor 3 is dependent on air flowrate and on the hydrophobic properties of the particles, and theirweight fraction in the feed slurry.

An immediate advantage of the ASH is the directed motion and intimatecontact between the particles in the swirl-layer on the porous vesselwall and the freshly formed air bubbles. The high centrifugal forcefield developed by the swirling slurry imparts more inertia to the fineparticles so that they can impact the bubble surface and attach to thebubbles. As a result, separation of fine particles is enhanced.

However, ASHs are relatively poor separators of coarser hydrophobicparticles because the velocity of the swirling slurry imparts too highan inertia to these particles, thus preventing these particles fromattaching to the air bubbles. As such, to achieve separation of thesecoarser particles, it is necessary that they exhibit relatively stronghydrophobicity so that the bubble/particle aggregate are stable underthe prevailing hydrocyclone conditions. In cases where hydrophobicity isnot strong enough, the system will exhibit some characteristics of aclassification cyclone in that the coarse hydrophobic particles will betransported by the slurry to the underflow discharge annulus, while thefiner particles will have a tendency to be transported into the frothcore and out through the overflow vortex finder.

Studies have shown that the separation efficiency for a number ofmineral particles falls as particle diameters increase above 100microns. However, other studies show that the upper particle size limitis strongly affected by the hydrophobicity of the particle (as discussedabove), and thus can be extended beyond 100 microns. For coal particles,testing shows that separations of particles above 100 to 400 micronsdrops significantly with increasing slurry pressure.

Therefore, an important addition to the art would occur if a method andapparatus is developed that can effectively separate particles of sizesbeyond the present range of particle sizes. Also, a significantimprovement would occur if increased slurry pressure (thereforeincreased feed flow rates) can be used while maintaining efficientseparation. An important development in the method and apparatus isdescribed in applicant's published application WO 91/15302 publishedOct. 17, 1991 with surprising degrees of particle separation involvingunique application of separation techniques in an ASH. As a guide infurther understanding the principles of separation in the new ASH ofapplicant, one may refer to the published PCT application. However, asan overview the following principles are discussed to provide a betterunderstanding of the benefits provided by applicant's discovery set outin this application.

A. Froth Flotation

As previously explained, separation of hydrophobic particles isaccomplished by separating the upper layer of the slurry which is in theform of a froth or foam from the remaining liquid. Froth flotation hasbrought applicability of the process with respect to particle size andits effective from 8 to 10 mesh below. More so than for any otherseparation process, flotation has almost no limitations in separatingminerals.

Flotation machines provide the hydrodynamic and mechanical conditionswhich effect the actual separation. Apart from the obvious requirementsof feed entry and tailings exit from cells and banks and for hydrophobicor mechanical froth removal, the cell must also provide for:

1. effecting suspension and dispersion of small particles to preventsedimentation and to permit contacting with air bubbles;

2. influx of air, bubble formation, and bubble dispersion;

3. conditions favouring particle bubble contact and attachment;

4. a non-turbulent surface region for stable froth formation andremoval; and

5. in some cases sufficient mixing for further mineral reagentinteraction.

The following lists some of the more important mechanisms occurring inflotation machines.

PULP: Bubble genecies; particle/bubble relative flow path; thinning andrupture of separating liquid films; highly aerated impeller region andless aerated remainder with intense recycle flow between two regions;steep pulp velocity gradients especially in the presence of frothingagent; distribution of residence time of solids.

FROTH: Concentration gradients arising from selective and clingingaction of froth column; bubble coalescence; concentration gradients maybe represented by layering with step-wise concentration changes and twoway mass transfer between the layers.

PULP-FROTH TRANSITION: Two-way solid and liquid mass transfer betweenphases.

AIR: Proves the motive force for both solids and water transfer frompulp to froth.

WATER: Transported by air and all solids non-selectively at increasingrate with decreasing particle size, into froth column, aids return ofsolids from froth and pulp by drainage.

The rate of flotation of particle by bubble can be expressed as theproduct of the probability of collision P_(c) between the particle andbubble, the probability of attachment P_(a) between the bubble andparticle, the probability of bubble with particle attachment enteringfroth P_(f), and the probability of bubble and particle remainingattached throughout the flotation process P_(s).

    K=P.sub.c ·P.sub.a ·P.sub.d ·P.sub.s

For the most part, the probability of attachment depends upon thesurface characteristics of the mineral and the degree of collectoradsorption on the mineral surface. It was shown that induction time forattachment decreases as the particle size decreases. Because of theshorter induction time, fine particle should float faster which does notexplain the observed decline in flotation efficiency for fine sizeparticles.

The probability of a particle remaining attached to a bubble dependsupon the degree of turbulence found in the system. The same forces thatdrove the particle and bubble together are available to separate them.It was shown that: ##EQU1## Where d_(p) is the particle diameter andd_(pmax) is the maximum diameter of a particle that will remain attachedunder the prevailing turbulent conditions. The probability is lowest forcoarse size particles and approaches unity for fine size particles. Onceattached the probability of remaining particles. Based on theseconsiderations, it appears that for fine particles the poor probabilityof collision is the main reason for the poor flotation. This means thatthe hydrodynamic forces are very important for flotation of fineparticles.

The probability of collision depends upon the number and size of theparticles and the bubbles and the hydrodynamics of the floatation pulp.This probability is directly related to the number of collisions perunit time and per unit volume. The number of collisions in flotationsystems can be represented by the formula:

    N.sub.c =5-N.sub.p ·N.sub.b ·r.sub.bp ·(V.sup.2.sub.b +V.sup.2.sub.p).sup.1/2

Where N_(p) is the number of particles, N_(b) is the number of bubbles,r_(bp) is the sum of the particles and the bubble radii, and V_(b) ² andV_(p) ² are a means square of the effective relative velocity betweenthe particles and bubbles. From the equation, it can be seen that byincreasing the number of bubbles and the relative velocity of thebubbles and particles, the number of collisions can be increased for agiven pulp.

The final factor affecting the flotation rate constant k is bubbleloading Bubble loading is not yet well understood, but it essentiallylimits the capacity of the bubbles to carry particles out of theflotation cell. As the feed rate increases for a given aeration rate,the bubbles become more fully loaded. When the bubbles become more than50% loaded, P_(s) decreases as the bubbles become particle residencetime on the bubble is shortened and as the available bubble surface forattachment is reduced. The net effect is a decrease in the volume of k.In addition, bubble loading may also influence the coalescence ofbubbles with the flotation cells, which would have a much morepronounced effect on k.

After the flotation rate constant, the retention time of particles inthe flotation cell has the most significant impact on flotationrecovery. Retention time is determine by dividing the effective volumeof the flotation cell (corrected for air hold-up) by the flow rate ofthe liquids in the slurry entering or exiting the flotation cell. Thusall three parameters, flotation cell volume, liquid slush/slurry flow,and air hold-up, play a role in determining the retention time of theflotation cells. Conventional froth flotation is very effective forparticles down to 20 micrometers in size, but the flotation efficiencydrops off as the particle size decreases below 20 micrometers.

B. Radial Gravity Separation

Gravity concentration may be defined as that process where particles ofmixed sizes, shapes, and specific gravities are separated from eachother by the force of gravity or by centrifugal force. The nature of theprocess is such that size and shape classification are an inherent partof the process in addition to separation on the basis of specificgravity from whence the process got the name. For coarse size minerals,efficient specific gravity separation has been possible for many yearswith open-bath vessels using the natural settling velocity or buoyancyof the particles. If vessel size remains within an economical limit, theparticles in the bath vessels must have high setting rate in a 1Ggravitational field. To extend a sufficient specific gravity separationof smaller sizes, the gravitational acceleration of particles isreplaced by artificial radial gravity field sometimes called centrifugalfield. The settling of small particles in a centrifugal force field issimilar to that found in a static bath except that the acceleration dueto gravity "g" is replaced by a radial gravity acceleration.

To date, the most effective use of this principle has been obtained withdevices that rotate a liquid or suspension within a stationary enclosurein order to create radial gravity force. When a slurry is injected intoa cylinder in an involuted manner, laminar circular flow will beachieved and heavier particles will be moved outward. This process willbe more effective if the flowing medium flows in a laminar manner. Thismeans that all particles in the slurry layer have the same angularvelocity and there is no relative movement of the particles in respectto each other. The only exception is slow outward drift of heavierparticles. After leaving the cylinder, the flow stream possessesparticle distribution by mass. Heavier particles are closer to thecylinder wall, while lighter particles are equally dispersed over astream volume.

C. Open Gradient Magnetic Separation

Open gradient magnetic separation (OGMS) is a generic term used todescribe any process involving magnetic separation achieved by particledeflection in non-uniform magnetic fields. OGMS is based on the magneticforce acting on a small particle in an inhomogeneous field and can bedescribed as:

    F.sub.m =V.sub.p J.sub.p ∇B.sub.o /μ.sub.o     ( 1)

where:

F_(m) is the magnetic force

V_(p) is the volume

J_(p) is the magnetic polarization of the particle

∇B_(o) is the gradient of the external magnetic field

μ_(o) is the permeability of the medium.

J_(p) can be express as: ##EQU2## where: X is the magneticsusceptibility of the particle;

D is the demagnetizing factor of the particle, and is 0<D<1; and

B_(o) is the magnetic flux density.

For para-magnetic particles, D<<1, therefore J_(p) ≅χB_(o), and equation(1) becomes:

    F.sub.m =V.sub.p χB.sub.o ∇B.sub.o /μ.sub.o (3)

For ferri- and ferro-magnetic particles, χ will be dependent on themagnetic field, and J_(p) usually reaches a saturation value, J_(ps), ina relatively low field. Therefore, from equations (1), (2) and (3), wecan see that efficient separation will occur if the magnetic fluxdensity B_(o), and its gradient ∇B_(o) are sufficiently high.

Hundreds of different kinds of magnetic separators have been constructedin the last two centuries. In these separators, the necessary magneticconditions are obtained either by using the field and the gradient of apermanent or an electromagnet, or by placing in the homogeneous fieldsecondary ferro-magnetic particles that give rise to field gradientsaround them. In the latter case, the gradients are often several ordersof magnitude higher than in the former, but the resulting force is ofshorter range because the maximum field is limited.

Open-gradient magnetic separators belong to the first group. The fieldand its gradient are produced by a suitable arrangement of magnets. Therange of the force is of the order of a few centimeters. The operatingprinciple of the separators is that a beam of particles flow through themagnetised area and is split into two or more parts. The force thatdeflects the particles is often modest, but due to the relatively longresidence time in the field, it provides a continuous separation withoutparticles being accumulated in the magnetized space.

The degree of success of OGMS depends upon the deflection imparted tothe particles. This, in turn, depends upon four factors:

(i) the particles themselves (size, magnetic susceptibility, density);

(ii) the retention time of separating forces acting on particles;

(iii) the magnitude and geometry of the non-uniform magnetic field; and

(iv) the geometry of magnetic and non-magnetic discharge posts.

One possible configuration provides for dry separation of ore particles,wherein the particles are made to fall through a magnetic field. As theparticles fall, they are deviated by their relative attraction to, orrepulsion from, the poles, and the resultant stream of ore is divided intwo or more components by separating boxes.

In wet-magnetic separators, one design requires the positioning of along rectangular channel adjacent to a magnet. The slurry is then fedthrough the channel, and separation occurs as the particles areinfluenced by the magnetic field.

Other types of OGMS are continuous units employing specially designedmagnets to generate strong field gradients in a relatively large, openworking volume, in which flowing slurry is effectively split intomagnetic and non-magnetic streams (GB Patent 1,322,229, Jul. 4, 1973).

A further type of OGMS is a helical flow superconducting magnetic oreseparator consisting of a superconducting dipole with a cylindricalannular slurry channel around one section [M. K. Abdelsalam, IEEETransactions on Magnetics, Vol. Mag. 23, No. 5, Sep., 1987]. Helicallyflowing particles are forced outward due to the centrifugal force, andthis is in turn opposed by magnetic forces on the magnetic particles.When a slurry flows helically in the annulus, non-magnetic particlesexperience a radially outward centrifugal force. Magnetic particles, onthe other hand, experience an inward magnetic force in addition to theoutward centrifugal force. Separation is thereby achieved if themagnetic force is strong enough to deflect the magnetic particlesinward.

In the latter arrangement, magnetic forces act in opposite directions tothe centrifugal forces, thereby substantially reducing the separationpower of the apparatus. When the magnetic force equals the centrifugalforce, no separation occurs since the magnetic particles do notexperience any deflecting force. Therefore, the magnetic force neededmust be substantially greater than the centrifugal forces generated inthe apparatus.

SUMMARY OF THE INVENTION

According to an aspect of the invention, a process for separatingparticles in a slurry based on different physical, magnetic and/orchemical properties of the particles, the slurry including a mixture ofsolid particles and/or liquid particles which are immiscible in theslurry. The process comprises:

i) introducing a stream of the slurry into a cylindrical chamber havinga cylindrical inner wall, the chamber being vertically oriented andclosed at its lower end and open at its upper end, the stream beingintroduced near the first end at an incline and tangentially of thechamber to develop a spiral flow of the stream along the chamber innerwall toward the open end,

ii) introducing the stream in sufficient volume and pressure to developa vortex in the slurry which extends downwardly from the chamber upperend,

iii) introducing air into the stream during at least a portion of itsupward travel, the air being introduced to the stream through meanslocated at the chamber inner wall and for developing the air bubbleswhich move into the stream,

iv) the chamber being of a height sufficient to provide a residence timein the chamber which permits a separation of particles on theirphysical, magnetic and/or chemical properties with at least lighterhydrophobic particles combining with air bubbles and moving inwardlytowards the vortex and at least heavier particles under influence ofcentrifugal forces of the spiral flow, moving outwardly towards thechamber inner wall, the stream developing into a whirlpool at thechamber upper end,

v) directing the whirlpool stream outwardly at the open end into a catchbasin surrounding the open end, the whirlpool stream swirling outwardlyas the stream flows into the catch basin having a liquid level proximatethe open end to permit the air bubbles to float toward a peripheral edgeof the catch basin,

vi) separating the floating air bubbles with lighter hydrophobicparticles from the heavier particles by collecting outwardly floatingair bubbles from an upper zone of the catch basin, while the heavierparticles sink downwardly of the catch basin and removing the heavierparticles from a lower zone of the catch basin to effect the separation.

According to another aspect of the invention, an apparatus forseparating particles in a slurry based on different physical, magneticand/or chemical properties of the particles, the slurry including amixture of solid particles and/or liquid particles which are immisciblein the slurry.

The apparatus comprises when in its vertical orientation:

i) a cylindrical tube defining an interior cylindrical chamber with acylindrical inner wall, and a closed lower end,

ii) the inner wall having along at least a minor portion thereof andextending therearound, means for introducing gas bubbles into the innerchamber as a liquid slurry passes over the gas introducing means,

iii) means for introducing a stream of slurry tangentially of andinclined relative to the inner wall, the stream introducing means beingpositioned in a lower zone of the chamber to direct a slurry stream in aspiral manner at the incline,

iv) a catch basin surrounding an open upper end of the chamber toreceive slurry overflowing the open upper end,

v) the upper end having a smoothly curved edge portion to facilitate asmooth transition in flow of the slurry from a vertical direction to anoutward direction as slurry overflows into the catch basin,

vi) means for collecting froth generated in the slurry by bubblesintroduced by the gas introducing means, the froth collecting meanssurrounding the catch basin, a weir being provided around the catchbasin to define an overflow for froth floating outwardly of the catchbasin, whereby froth overflowing the weir is collected in the frothcollecting means,

vii) the catch basin having an outlet in its lower portion to permitremoval of sinking particles of liquid,

viii) the froth collecting means having an outlet to permit removal offroth from the collecting means,

ix) the catch basin outlet having means for controlling flow of liquidto maintain in the catch basin an acceptable height of liquid to permitfroth to overflow the weir.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are shown in the drawings whereinFIG. 1 is a perspective view of the apparatus for effecting a separationof particles in a liquid slurry.

FIG. 2 is a section along the lines 22 of the conduit for introducingslurry to the separation apparatus of FIG. 1.

FIG. 3 is a perspective view of the apparatus of FIG. 1 with portionsthereof removed to show certain details of the apparatus.

FIG. 4 is a longitudinal section of the apparatus of FIG. 1.

FIG. 5 is a detail of the section of FIG. 4 demonstrating the vortex ofslurry located therein.

FIG. 6 is an enlarged portion of FIG. 5 showing contact of gas bubbleswith particles in the slurry.

FIG. 7 is an alternative embodiment of the invention showing thepositioning of magnets to develop a magnetic field within the separator.

FIG. 8 is a section along the lines 88 of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred aspects of the invention will be discussed with reference toembodiments shown in the drawings, however it is appreciated that theprocess of this invention may be implemented in a variety of ways toachieve separation of different types of particles in the incomingslurry stream. We have found that the process and apparatus of thisinvention is particularly suitable for separating slurries containingliquid hydrocarbons and in particular mixtures of bitumen with bitumencovered sands. The process is equally applicable to separation ofmineral ores, coal and other particulate systems which may be carried inan aqueous or other liquid vehicle.

Unlike the system of applicant's published PCT application WO91/15302the process and apparatus according to this invention provides for anupward flow of the slurry with consequent migration of bubbles to theinside of the vortex where at the open upper end of the separationchamber the stream is allowed to overflow in a manner which provides forcontinued flotation of the air bubbles. Hence, separation is effected bycentrifugal and/or magnetic forces acting on the stream followed byprinciples of separation by flotation of bubbles to form a froth therebyseparating particles attached to the bubbles from particles which remainin the slurry stream which have overflowed into the catch basin.

With particular reference to FIG. 1, the apparatus 10 comprises acylindrical chamber 12 which when in use is vertically oriented. Theslurry to be introduced into the system is directed under pressure inthe direction of arrow 14 through conduit 16 which is rectangular incross-section. Conduit 16 is positioned tangentially of an inclinerelative to the cylindrical chamber 12. The lower end 18 of the chamber12 is closed so that all fluids introduced to the chamber 12 flowsupwardly to the open end 20 of the chamber. The liquid is allowed tooverflow the upper edge 22 of the chamber into a catch basin 24. Thecatch basin defines an annular cavity 26 which is filled with treatedslurry. Froth, as it overflows from the central portion of the centralchamber 20, flows over the weir 28 defined by the peripheral edge of thecatch basin 24 and is collected in a froth collector 30. The outlet 32is provided in the catch basin 24 for removal of particles which sink.The froth which overflows and is collected in the froth collector 30 isremoved through outlet 34 defined by conduit 36. Connected to outlet 32is conduit 38 which includes a valve 40. The valve 40 is adjusted tomaintain adequate liquid level in the catch basin 24 to provide foroverflow of froth over the weir 28.

Located circumferentially of the cylindrical inner chamber 12 is aplenum 42. Pressurized air is introduced in the direction of arrow 44through inlet 46. Pressurized air, as will be discussed in FIG. 2,enters through a porous mesh to introduce bubbles into the slurry as itflows upwardly of the cylindrical chamber 12.

The stream of slurry is preferably injected in a manner which reducesturbulence in the introduced stream. To approximate laminar flow therectangular conduit 16 as shown in FIG. 2 may include flow straighteningveins 19 which extend longitudinally of the conduit 16 to reduceturbulence in the stream before introduction to the chamber 12. Ideally,the stream approximates laminar flow as the stream exits the conduit 16.However, it is appreciated that for certain types of separation, mildturbulence in the flow is acceptable while achieving the desired degreeof separation.

For any particular diameter of cylindrical reactor the conduit 16 isfixed relative to the cylindrical chamber 12. FIG. 3 demonstrates inprinciple how the relative incline of the conduit 16 can be adjustedvertically in the direction of arrows 48 or 50. Variation in inclinedetermines the angle at which the stream 52 progresses upwardly of theinside wall 54 of the cylindrical chamber 12. Ideally, the spiral stream52 progresses upwardly of the inner cylindrical wall of the chamberwithout intersecting its adjacent lower portion of the spiral asdesignated at 52a. This ensures a continued upward travel of the streamin a spiral manner while minimizing turbulence in the flow of thestream.

As the stream progresses upwardly of the inner circular chamber airbubbles are introduced into the stream to effect a separation ofparticles which are attracted to the air bubbles. It is appreciated thata variety of gas bubble introduction mechanisms may be provided whichcommunicate with the inner surface of the cylindrical chamber. Forpurposes of discussion and illustration with this particular embodimentof FIG. 3, the plenum 42 envelops a fine mesh 56. Air is introducedthrough tube 46 and pressurizes the chamber within the plenum 42 wherebyair slowly diffuses through the porous mesh 56 to introduce bubbles intothe slurry stream in a manner to be discussed in more detail withrespect to FIGS. 5 and 6. As will become more apparent with respect tothe discussion of the embodiment of FIG. 4, the stream as it emergesfrom the upper end 20 of the cylindrical chamber 12 is allowed tooverflow into the annular recess 26 of the catch basin 24. To providefor a smooth transition in the flow of the stream from the verticalorientation to an outward orientation the upper edge 58 of thecylindrical chamber 12 is smoothly curved so as to minimize turbulencein the stream as it changes direction in flow. By minimizing theturbulence induced into the transition phase for the stream flow, thefroth which collects on the inside of the swirling layer remainsfloating as indicated by arrow 60 and thereby overflows the weir edge 28whereas the heavier particle or particles in the slurry which are notattached to the air bubbles flows downwardly in direction of arrow 62.The particles then carried with the froth overflowing weir 28 areremoved in a direction of arrow 64 for subsequent processing and/ordiscard. Similarly, the heavier particles which are carried downwardlyin a direction of arrow 62 are removed in the direction of arrow 66 forprocessing and/or discard. In this manner a very simple yet effectivecollection of the desired particles either in the material which floatswith the air bubbles and flows over into the froth collector 30 or theheavier particles which are retained in the catch basin 24 are therebyseparated and recovered.

As shown in FIG. 4 a preferred construction for the separator apparatusis shown in section. The cylindrical chamber 12 has an inner cylindricalwall 68 which, when the apparatus is in use extends vertically as shownin FIG. 4. The lower end 18 of the cylindrical chamber is closed by acircular plate 70 so that all fluids or liquids introduced into thecircular chamber 12 flow upwardly to the open end 20 of the cylindricalchamber. As already explained, the conduit 16 for introducing the slurrystream is inclined so that the stream 52 flows upwardly in a spiralmanner confined by the circular inner surface 68 of the cylindricalchamber 12. The incline of the conduit 16 is such to ensure that thestream 52 spirals upwardly without interfering with the lower adjacentstream to minimize turbulence in the stream as it flows upwardly.

As a continuation of the inner surface 68 of the cylindrical chamber thefine mesh generally designated 56 is flush with the inner surface 68 todefine a continuing inner surface 68a. The plenum 42 is defined by anouter shell 72 which encloses the hollow cylinder of fine mesh 56. Theshell 72 defines an annular plenum 74 into which the pressurized air isintroduced through inlet 46. Sufficient air pressure is developed inplenum 74 to cause the air to slowly diffuse through the fine mesh 56 inthe direction of arrows 76 thereby introducing air bubbles into theupwardly flowing stream 52 of the slurry.

The slurry is introduced through conduit 16 in sufficient volume and atsufficient velocity to develop at least in the upper zone, generallydesignated 78, a vortex, generally designated 80. With sufficient volumeand/or velocity vortex 80 may extend from the upper zone 78 of thecircular chamber down to the lower zone 82 of the cylindrical chamber.As shown in FIG. 4, the inner surface 84 of the vortex is formedprimarily of the air bubbles which have migrated towards the center ofthe spiral stream, that is, the inner surface 84 of the vortex.Schematically, the developed inner annular layer of bubbles is definedby region 86 whereas the outer layer of slurry liquid containing atleast the heavier particles is designated 88. By way of this cylindricalchamber, an air-sparged separation of particles in the introduced slurryis achieved. Quite surprising as discovered in accordance with thisinvention, a smooth transition of the vertically oriented flow of slurryto an outward flow allows the innermost froth layer 86 to continue in anundisturbed manner and overflow into the froth collector 30. Withreference to FIG. 4, the upper edge 22 of the cylindrical chamber isdefined by a cap 90 which according to this embodiment is a continuationof the shell 72 into the inner surface 92 for the inner wall 68. Theinner surface 92 is then continuous with the fine mesh 56. To seal offthe annular plenum 74 a suitable plug material 94 is provided or atleast a plate 96 to close off the plenum 74. The lower end of the plenum74 is closed off by the annular shaped plate 98. The shell material 72is shaped to define a smoothly rounded end portion 100. As shown in FIG.4 the smoothly rounded portion is parabolic is cross-section andcomprises an inner edge portion 102, an upper edge portion 104 and anoutside edge portion 106 The shell 72 is shaped at 108 to provide a lip110 for the smoothly rounded upper edge portion 22. As shown in FIG. 4the innermost layer 86 progresses smoothly from a vertical orientationin travel to an outward orientation in travel as indicated by arrow 112so that the froth layer 114 floats over the weir edge 28 into the frothcollector 30 in the direction of arrow 60. As the froth layer 114traverses outwardly over the catch basin 24, the liquid level 116, asretained in the catch basin 24, allows for additional gas bubbles tofloat upwardly into layer 114 to further enhance the froth flotation ofattached particles from the remaining particles in the liquid 116.Hence, the radial extent of the catch basin 24 may be varied to enhancethe separation of the froth layer, it being understood however that theextent of the radial distance for the catch basin cannot extend beyondthe distance which the froth travels due to the transition in flow ofthe froth from a vertical orientation to an outward orientation.

As is appreciated by those skilled in the art, the level of liquid 116in the catch basin 24 may be sensed by sensor 118. Sensor 118 canprovide output which is connected to controller 120 via input line 122.Controller 120 has output via line 124 to servo control valve 40. Bystandard feedback techniques the controller 120 opens and closes thevalve 40 so as to maintain the desired liquid level in the catch basin24 to optimize the collection of froth overflowing the weir 28.

As schematically shown in FIG. 4 the stream 52 spirals upwardly of thecircular chamber 12. The inclination of the conduit 16 is such to ensurethat the spiral flow does not interfere with adjacent layers. However,the flow of liquid is such that distinct ribbons of flow is not per sevisible. Instead, the stream melts together to form an annularcylindrical layer of slurry travelling upwardly along the inner surface68 of the inner cylindrical chamber. Hence, a top view of the unit 10 inoperation reveals a whirlpool-like flow for the stream as the liquidflows upwardly of the inner wall of the chamber and transforms from anupward flow to an outward flow of the liquid. As the whirlpool expandsover the upper edge 100 of the open end of the cylindrical chamber, thefroth spirals outwardly towards the weir 28. Correspondingly, the liquidspirals downwardly of the catch basin 24 towards the outlet 32. Byvirtue of this smooth transition in the froth layer from an upward flowto an outward flow quite surprising, as will be demonstrated by thefollowing Examples, very high recoveries of desired particles from theslurry mixture is achieved.

With reference to FIG. 5 the development and incorporation or inclusionof air bubbles in the stream is discussed. Pressurized air in plenum 74migrates or diffuses through the fine mesh 56 to develop at the meshinner surface 68a minute bubbles 126. The slurry stream as it flowsupwardly in a direction of arrow 52 develops a thickness 128circumferentially around the vessel inner wall 68a. The vortex 80extends centrally of the cylindrical chamber along the longitudinal axis130 of the chamber. The innermost surface of the slurry is thereforedefined by the inside surface 84 of the vortex. Air is introducedthrough the fine mesh or porous vessel wall and is sheared into numerousbubbles by the high velocity swirl of the slurry as shown in FIGS. 5 and6. The bubble generation mechanism accomplished by the fine mesh 56 is atwo-stage process. Air migrates through the micro channels of the porouscylinder 56 as shown at 132. When leaving the pore, air creates a smallcavity 134 in the slurry as shown in FIG. 6. The cavity grows until thesurface tension is smaller than the shearing force of the flowingslurry. Once a bubble 126 is sheared off from the surface 68a of thecylinder, it begins to flow with the slurry at the same speed asparticles in the slurry. The radial gravity force creates an upwardhydrostatic pressure. This causes the bubble to move towards the innersurface 84 of the slurry in the direction of arrow 136. The bubblepossesses velocity which has two components: 1) tangential componentwhich is equal to the tangential velocity of slurry; and 2) radialvelocity which is due to the buoyancy. This means that the bubbletravels perpendicularly to the motion of the slurry thereby increasingthe probability of collision with particles in the slurry. The radialgravity field creates relatively high pressure in the slurry. Thebubbles will move relatively fast towards the vortex 80 in the centre ofthe cylinder. The bubbles collide with the particles, and at leasthydrophobic particles become attached to the bubbles. Thebubble-particle agglomerate 140 is transported radially towards theinner surface 84 of the slurry layer and travels upwardly in thedirection of arrow 138. On the other hand, the hydrophillic particles142 generally remain radially outwardly of the slurry layer, and thuscontinue to move in the swirl direction along the porous vessel wall 68auntil they are discharged at the upper end of the vessel.

The fine mesh 56 which constitutes the porous portion of the vessel wall12 may be constructed of a variety of materials. The fine mesh may be ascreen product having rigidity and which defines a reasonably smoothsurface 68a to maintain centrally laminar flow in the slurry. A varietyof screen meshes are available which will provide such porosity. Othermaterials include sintered porous materials of metal oxides which havethe necessary structural strength yet provide a relatively smoothsurface 68a. It is appreciated that other forms of porous materials areavailable such as sintered, porous, stainless steel of controlledporosity, for example, 316LSS. To enhance the separation of theparticles 142 from particles 144 having different characteristics, amagnetic field may be used where the particles may having para-, ferri-or ferro-magnetic characteristics. With reference to FIG. 7 and 8, amagnetic field is produced in the cylindrical chamber 12 which extendsalong its length. The magnets which produce the magnetic field may belocated in the plenum 74. According to FIG. 7 and 8, four magnets 146,148, 150 and 152 are provided. The quadrapole configuration for themagnets develops a magnetic field indicated by arrows 154 which attractferri- and ferro- magnetic particles towards the inside surface 68a ofthe cylindrical chamber 12.

The poles of the magnets are oriented toward the axis 130 of theapparatus, and the quadrapole configuration provides radial magneticfield 154 with no components along the axis 130 and with a net magneticfield at the centre 130 of the vessel equal to zero. It is appreciatedthat the magnetic field can be created by either permanent magnets or byelectromagnets. The operation of the apparatus in a magnetic fieldrequires, as already described, that the slurry be introduced into thecylindrical vessel through the tangential inlet 16. The slurry forms thelayer on the inside surface 68a of the porous wall. Air is continuouslysparged through the porous wall and into the thin swirl layer. Bubblesform in the slurry collide with the particles in the slurry and formbubble particles aggregate with the hydrophobic particles of the slurry.Due to the circular motion of the slurry and due to the radial geometryof the magnetic field and magnetic field gradient, the slurry flow isalways perpendicular to the magnetic force and to the flow of bubbles.Generally, there are two different forces acting on a hydrophillicpara-magnetic or ferromagnetic particle in the slurry. It will beappreciated that any solid particle placed in a magnetic field will beaffected by it in some way. Solids may be classified into threecategories depending on their magnetic properties:

1. diamagnetic particles, which are repelled by a magnetic field;

2. para-magnetic particles, which are attracted by a magnetic field; and

3. ferro-magnetic particles, which are most strongly attracted by amagnetic field.

Although the process of this invention is particularly suited to theseparation of discrete solid particles in coal and/or minerals, theprocess may also be used to separate biological particulate matter suchas cells, labelled proteins and fragments thereof, solid and semi-solidwaste materials and the like, particularly when magnetic particles areemployed in the separation process.

During operation of a flotation apparatus, there are generally twoforces acting on the hydrophillic paramagnetic or ferro-magneticparticles. These two forces are the centrifugal force, F_(c), and themagnetic attraction force, F_(m). The centrifugal force is due to theswirling motion of the slurry along the inside porous wall of thevessel, whereas the magnetic attraction force is due to the magneticforce of the quadrapole magnet acting on the particles perpendicularlyto the flow of the slurry. These two forces act in the same direction,that is, radially towards the outside of the cylindrical vessel.Therefore, the total force acting on the hydrophillic and/or magneticparticles is the sum of the centrifugal force and the magneticattraction force, and it acts radially outwards of the vessel. Theseresultant forces cause these particles to remain in the swirl-layer andto be eventually discharged into catch basin 24. On the other hand,there are generally three forces acting on the hydrophobic anddiamagnetic particles that have become attached to the air bubbles.These three forces are:

1. the hydrostatic force F_(h) ;

2. the magnetic repelling force, F_(r) ; and

3. the centrifugal force, F_(c).

The hydrostatic force is the force of the air bubble/particle aggregatethat causes it to be transported radially inwardly towards thecylindrical axis. The magnetic repelling force, due to the quadrapoleconfiguration of the magnet, acts on these particles in a directionradially inwardly towards the cylindrical axis. The third of theseforces, the centrifugal force, is due to the swirling motion of theslurry, and acts on the particles in a radially outward direction fromthe cylindrical axis. For hydrophobic and diamagnetic particles that arenot too large and have a specific gravity smaller than those ofhydrophillic, the hydrostatic and magnetic repelling forces are greaterthan the centrifugal force, thereby causing a net force acting on theseparticles inwardly towards the cylindrical axis of the vessel. Thisresultant force causes these particles to be transported upwardly withthe swirl inner layer of froth.

From the above, it will be appreciated that the present invention canadditionally provide magnetic repelling forces acting on the hydrophobicand diamagnetic particles, thereby allowing for efficient separation ofsmaller sized hydrophobic particles from the larger sized particles.Similarly, the addition of a magnetic attraction force acting on thehydrophillic para-magnetic or ferro-magnetic particles allow for theefficient separation of finer hydrophillic particles which wouldotherwise have been entrained by the air bubbles out of the swirl layerand into the froth core.

Hence, on the hydrophobic and diamagnetic particles which have formedaggregates with the air bubbles, there are generally three forces actingon them. They are the hydrostatic or buoyancy force, F_(h), which is theforce transporting the bubble particle aggregate towards the innersurface of the slurry stream, the magnetic repelling force, F_(r), andthe radial gravity force F_(c). The hydrostatic and the magnet repellingforces act on the particles in a radially inward direction whereas thecentrifugal force acts on the particles in a radial outward direction.The combined action of these three forces is a net force acting radiallyinward towards the centre of the cylindrical vessel.

The above described process is more efficient when the medium or slurryflows in laminar manner. The laminar flow is characterized by constantangular velocity for all flowing medium particles, and by no significantrelative movement of particles in respect to each other. Turbulent flowis characterized by the distribution of particle velocities (moduli anddirections), with a mean value parallel to flow. The laminar velocity ofparticle will have two components, V₁ parallel and V₂ perpendicular.These two components create a spiral flow of medium in the form of theswirl layer. When the swirl layer reaches the upper end of the cylinder,the vessel wall no longer contains the swirl flow so that the slurrystream transforms to an outward flow in a spiral manner.

The apparatus according to this invention can be modified depending uponthe type of particles to be separated. It has been found that thisapparatus has been particularly effective in causing a separation ofbitumen from tar sands. A slurry is developed which includes water,particles and viscous fluid comprising sand and bitumen. The systemaccording to this invention can provide up to 80% recovery of thebitumen compared to considerably lower recoveries in the range of 30%for separation apparatus such as disclosed in applicant's published PCTapplication WO91/15302. With this apparatus the separated material stayson top and flows over the edge of the catch basin. In this way the airwhich has been sheared into the slurry now works entirely towardsrecovery during the additional flotation stage achieved in the catchbasin. It has been found that for every unit volume of slurry treatedapproximately two volumes of air can be introduced to the slurry whichprovides a fairly high ratio of air to slurry. It is appreciated ofcourse that wherever or whenever air is mentioned in the specificationthat other gases may be substituted for air depending upon the types ofparticles to be treated. It is also appreciated that the diameter of thetreatment chamber may vary depending upon the required throughput andtypes of materials to be separated. Tests have demonstrated thatdiameters in the range of 2 inches, 4 inches, 6 inches and greater canbe used to process very high flow rates of slurry such as in the rangeof 2.2 liters per second for a chamber diameter of 2 inches. It isunderstood that the system may be developed and rendered mobile bymounting the system in a suitable trailer or railroad car.

The following data demonstrates the efficacy of this system as appliedin the recovery of various types of particles such as coal and bitumen.

EXAMPLE NO. 1

The "run of the mine" medium volatile butiminuous coal was screened and-100 mesh fraction was collected. A 2500 1 batch of sluury was prepared@5% by wt. solids. 1200 ppm kerosene and 1500 ppm of MIBC were added tothe slurry. The slurry was run through a 2 inch diameter separator unitof FIG. 4, the diameter being that for the internal diameter of chamber12. The slurry was introduced to the unit through conduit 16 at the rateof 1.2 l/s with the air flow through the porous wall 56 in the range of2 l/s. The concentrate adn tailings were collected and analyzed.

The following table summarizes the average performance with comparisonto recovery from a standard mechanical froth flotation cell operatedunder normal conditions.

    ______________________________________                                                     Feed                                                                          Sample                                                                              Concentrate                                                                              Recovery                                        ______________________________________                                        Average unit performance                                                                     12%     8%         86-88%                                      according to this invention                                                   Average froth flotation                                                                      12%     7.5%       85%                                         performance for the same                                                      coal in a standard froth                                                      flotation cell                                                                ______________________________________                                    

EXAMPLE NO. 2 Illinois No. 6 Coal

The same procedure of Example 4 was performed with prescreened IllinoisNo. 6 coal. The following table summarizes the performance of the unitof this invention.

    __________________________________________________________________________    Feed Sample (52)                                                              Fraction size                 Pyritic                                                                            Heating                                    based on screen                                                                         Direct Ash  Sulfur  Sulfur                                                                             Value                                      mesh sizing                                                                             (Wt %) (Wt %)                                                                             (Wt %)  (Wt %)                                                                             (Btu/lb)                                   __________________________________________________________________________    100 M retained                                                                          19.9   9.88 3.74    1.18 12682                                      400 M retained                                                                          55.5   8.37 3.74    1.09 12775                                      400 M passing                                                                           24.6   16.46                                                                              4.08    1.80 11608                                      TOTAL     100.00 10.66                                                                              3.82    1.28 12469                                      __________________________________________________________________________    Product Sample (60)                                                           Feed Rate = 1.10 l/s to unit Kerosene = 2875 ppm                              Air Rate = 2 l/s to unit MIBC = 1150 ppm                                                                       Yield in                                     Size Fraction          Pyritic                                                                            Heating                                                                            Required                                                                           Energy                                  of Recovered                                                                          Direct                                                                             Ash  Sulfur                                                                             Sulfur                                                                             Value                                                                              Stream                                                                             Recovery                                Stream  (Wt %)                                                                             (Wt %)                                                                             (Wt %)                                                                             (Wt %)                                                                             (Btu/lb)                                                                           (Wt %)                                                                             (%)                                     __________________________________________________________________________    100 M retained                                                                        9.8  7.15 3.13 0.75 13210                                                                              35.8 38.2                                    400 M retained                                                                        63.6 6.55 2.98 0.78 13625                                                                              83.2 86.4                                    400 M passing                                                                         26.6 8.18 3.37 1.22 12865                                                                              78.5 87.0                                    TOTAL   100.0                                                                              7.04 3.10 0.89 13153                                                                              72.6 76.6                                    __________________________________________________________________________

EXAMPLE NO. 3 Tar Sands

The 25% solids slurry of medium grade Athabasca tar sans was prepared at55° C. The slurry was then pumped through the 2" of FIG. 4 at the rateof 1.73 l/s with 3.4 l/s of air. The flow rate of concentrate (60) andtailing stream (62) was measured and samples were collected andanalyzed. The performance of the unit is summarized in the followingtable.

    ______________________________________                                                                             %                                        Slurry Makeup     % Bitumen % Water  Solids                                   ______________________________________                                        Average Concentrate Content                                                                     36.7      38.8     24.6                                     (% by wt)                                                                     Bitumen Recovery in Stream (60)                                                                 88%                                                         Solids Rejection in Stream (62)                                               ______________________________________                                    

EXAMPLE NO. 4 Graphite

A 27% solids slurry containing graphite, chalcopirite, pentlandite,phyrotite and rocks was fed to a 4" ID chamber 12 of FIG. 4 at the rateof 31 Gpm and 4 cfm of air. The following table summarized the averageperformance.

    ______________________________________                                                       Content % by                                                                  wt. in respective                                              Stream Component                                                                             stream       Recovery %                                        ______________________________________                                        COPPER                                                                        Feed (52)      0.73                                                           Concentrate (60)                                                                             0.62         45                                                Tails (62)     0.87         55                                                NICKEL                                                                        Feed (52)      4.09                                                           Concentrate (60)                                                                             3.14         41                                                Tails (62)     5.25         59                                                FERRUM                                                                        Feed (52)      123.3                                                          Concentrate (60)                                                                             9.7          41                                                Tails (62)     16.3         59                                                SULPHUR                                                                       Feed (52)      9.2                                                            Concentrate (60)                                                                             7.1          41                                                Tails (62)     12.0         59                                                CARBON                                                                        Feed (52)      20.2                                                           Concentrate (60)                                                                             43.8         73                                                Tails (62)     15.4         26                                                ______________________________________                                    

Although preferred embodiments of the invention are described herein indetail, it will be understood by those skilled in the art thatvariations may be made thereto without departing from the spirit of theinvention or the scope of the appended claims.

We claim:
 1. A process for separating particles in a slurry based ondifferent physical, magnetic and/or chemical properties of saidparticles, said slurry including a mixture of solid particles and/orliquid particles which are immiscible in said slurry, said processcomprising:i) introducing a stream of said slurry into a cylindricalchamber having a cylindrical inner wall, said chamber being verticallyoriented and closed at its lower end and open at its end, said streambeing introduced near said closed lower end at an incline end andtangentially of said chamber to develop a spiral flow of said streamalong said chamber inner wall toward said open end, ii) introducing saidstream in sufficient volume and pressure to develop a vortex in saidslurry which extends downwardly from said chamber upper end, iii)introducing air into said stream during at least a portion of its upwardtravel in said chamber, said air being introduced to said stream throughmeans located at said chamber inner wall and for developing said airbubbles which move into said stream, iv) said chamber being of a heightsufficient to provide a residence time in said chamber which permits aseparation of particles on their physical, electrical and/or chemicalproperties with at least lighter hydrophobic particles combining withair bubbles and moving inwardly towards said vortex and at least heavierparticles under influence of centrifugal forces of said spiral flow,moving outwardly towards said chamber inner wall, said stream developinginto a whirlpool at said chamber upper end, v) directing said whirlpoolstream outwardly at said open end into a catch basin surrounding saidopen end, said whirlpool stream swirling outwardly as said stream flowsinto said catch basin having a liquid level proximate said open end topermit said air bubbles to float toward a peripheral edge of said catchbasin, vi) separating said floating air bubbles with lighter hydrophobicparticles from said heavier particles by collecting outwardly floatingair bubbles from an upper zone of said catch basin, while said heavierparticles sink downwardly of said catch basin and removing said heavierparticles from a lower zone of said catch basin to effect saidseparation.
 2. A process of claim 1, further comprising directing saidstream whirlpool over a smoothly curved upper edge of said chamber upperend as said whirlpool stream swirls outwardly in changing from avertical direction of flow to an outward direction of flow.
 3. A processof claim 2, wherein said smoothly curved upper edge is parabolic incross-section whereby direction of flow is gradually converted fromvertical to an outward direction.
 4. A process of claim 1, wherein airis introduced along a major portion of its upward travel in saidchamber.
 5. A process of claim 4, wherein said air is introduced througha fine mesh to develop minute air bubbles in said stream.
 6. A processof claim 1, wherein said stream is introduced at sufficient volume andpressure to develop said vortex from said chamber upper end down towhere said stream is introduced.
 7. A process of claim 6, wherein saidstream is introduced as a thin stream which is rectangular incross-section.
 8. A process of claim 7 wherein said stream is introducedthrough a rectangular shaped channel, said channel being positionedtangentially to and at an incline to said chamber inner wall.
 9. Aprocess of claim 8 wherein flow straightening vanes are provided in saidchannel.
 10. A process of claim 9 wherein said stream is introduced at avolume and a pressure to provide a laminar flow in said channel.
 11. Aprocess of claim 2 wherein said catch basin has an outlet in said lowerregion, said sinking heavier particles being removed through saidoutlet, controlling flow through said outlet to maintain said liquidlevel proximate said upper edge to ensure thereby smooth transition ofstream flow from a vertical direction to an outward direction, saidsmooth transition permitting said bubbles located nearest said vortex toretain their relative position with respect to said heavier particlesand float on said liquid in said catch basin.
 12. A process of claim 11wherein said floating bubbles are collected by permitting a frothdeveloped by said floating bubbles to swirl outwardly over acircumferential weir provided around said catch basin peripherycollecting overflowing froth in a froth collector provided around saidweir.
 13. A process of claim 11 wherein said stream is inclined at anangle which causes said stream to contact its adjacent lower portion ofsaid spiral flow to provide thereby coverage of said chamber innersurface.
 14. A process of claim 1 for separating a slurry comprisingbitumen and tar sands.
 15. A process of claim 1 for separating a slurrycomprising mineral ore particles.
 16. A process of claim 1 forseparating a slurry comprising liquid hydrocarbons in water.
 17. Aprocess of claim 1 wherein a magnetic field is provided along saidchamber to attract magnetizable particles toward said column inner wall.18. Apparatus for separating particles in a slurry based on differentphysical, magnetic and/or chemical properties of said particles, saidslurry including a mixture of solid particles and/or liquid particleswhich are immiscible in said slurry, said apparatus comprising when inits vertical orientation:i) a cylindrical tube defining an interiorcylindrical chamber with a cylindrical inner wall, and a closed lowerend, ii) said inner wall having along at least a minor portion thereofand extending therearound, means for introducing gas bubbles into saidinner chamber as a liquid slurry passes over said gas introducing means,iii) means for introducing a stream of slurry tangentially of andinclined relative to said inner wall, said stream introducing meansbeing positioned in a lower zone of said chamber to direct a slurrystream in a spiral manner at said incline, iv) a catch basin surroundingan open upper end of said chamber to receive slurry overflowing saidopen upper end, v) said upper end having a smoothly curved edge portionto facilitate a smooth transition in flow of said slurry from a verticaldirection to an outward direction as slurry overflows into said catchbasin, vi) means for collecting froth generated in said slurry bybubbles introduced by said gas introducing means, said froth collectingmeans surrounding said catch basin, a weir being provided around saidcatch basin to define an overflow for froth floating outwardly of saidcatch basin, whereby froth overflowing said weir is collected in saidfroth collecting means, vii) said catch basin having an outlet in itslower portion to permit removal of sinking particles and liquid, viii)said froth collecting means having an outlet to permit removal of frothfrom said collecting means, ix) said catch basin outlet having means forcontrolling flow of liquid to maintain in said catch basin an acceptableheight of liquid to permit froth to overflow said weir.
 19. Apparatus ofclaim 18, wherein said stream introducing means comprises a rectangularin cross-section conduit extending through said chamber inner wall andtangentially of said inner wall, said conduit being inclined relative toa horizontal plane extending at 90° relative to a longitudinal axis ofsaid chamber.
 20. Apparatus of claim 19 wherein said incline ranges from10° to 25° from said horizontal plane.
 21. Apparatus of claim 19 whereinsaid means for introducing gas bubbles comprises a fine mesh around saidinner wall and along a portion of said inner wall.
 22. Apparatus ofclaim 21 wherein said fine mesh extends along a major portion of saidinner wall.
 23. Apparatus of claim 21 wherein said cylindrical chamberis surrounded by a plenum to enclose said fine mesh, means forpressurizing gas in said plenum to develop gas bubbles at said innerwall.
 24. Apparatus of claim 18 wherein said smoothly curved edgeportion is parabolic in cross-section.
 25. Apparatus of claim 24 whereinsaid froth collecting means is an annular trough for receivingoverflowing froth, said trough sloping towards said froth outlet toprovide collection of froth.
 26. Apparatus of claim 18 wherein saidcatch basin is sloped towards said catch basin outlet, means for sensingliquid level in said catch basin, said sensing means having input tosaid flow controller to varying flow proportional to height in saidcatch basin to maintain thereby a desired height of liquid in said catchbasin during flow of slurry along said chamber.
 27. Apparatus of claim18 wherein means for producing a magnetic field along said chamber isprovided outside said inner wall, said magnetic means attractingmagnetizable particles toward said inner wall.